The present invention relates generally to gas turbine engines, and, more specifically, to combustors therein.
In a gas turbine engine, air is compressed in a compressor and mixed with fuel in a combustor and ignited for generating hot combustion gases which flow downstream through one or more turbine stages which extract energy therefrom. Performance of the combustor affects engine efficiency and exhaust emissions. Mixing of fuel and air in turn affects combustor performance, and the prior art is crowded with combustor designs having varying degrees of effectiveness since many tradeoffs are typically required in combustor design.
Undesirable exhaust emissions include unburned hydrocarbons, carbon monoxide (CO), and nitrogen oxides (NOx). These exhaust emissions are affected by uniformity of the fuel and air mixture and amount of vaporization of the fuel prior to undergoing combustion. A typical gas turbine engine carburetor which mixes the fuel and air includes a fuel injection nozzle mounted in a swirl cup attached to the upstream, dome end of the combustor. The swirl cup typically includes two rows of swirl vanes which operate either in co-rotation or counter-rotation for swirling air around the injected fuel for forming a suitable fuel and air mixture which is discharged into the combustor for combustion.
Gas turbine engine carburetors vary in configuration significantly depending upon the specific engine design, and whether the engine is configured for aircraft propulsion or for marine and industrial (MandI) applications. NOx emissions are typically reduced by operating the combustor with a lean fuel and air mixture. However, lean mixtures typically result in poor low power performance of the combustor, increased CO and HC emissions, and are susceptible to lean flame blowout (LBO), autoignition, and flashback.
NOx emissions may also be reduced by configuring the combustor with a multiple dome, such as a double dome having two radially spaced apart rows of carburetors operated in stages. For example, the radially outer carburetors are sized and configured for pilot performance and operate continuously during all modes of engine operation from idle to maximum power. The radially inner carburetors are sized and configured for main operation and are fueled only above idle for higher power operation of the engine.
Accordingly, the required amount of fuel for operating the combustor over the different power settings may be selectively split between the outer and inner carburetors for obtaining suitable combustor performance with reduced exhaust emissions.
Performance of the combustor is also evaluated by conventional profile factor and pattern factor which indicate relative uniformity of radial and circumferential temperature distribution from the combustion gases at the exit of the combustor which affect efficiency and life of the high pressure turbine which firstly receives the combustion gases from the combustor.
A typical swirl cup used in both the outer and inner carburetors includes a tubular member in the form of a venturi disposed between the two rows of swirl vanes. The venturi has two primary purposes including a throat of minimum flow area sized for accelerating the injected fuel and swirl air from a primary row of swirl vanes to a suitably high velocity to reduce carbon formation on the face of the fuel injection nozzle and to prevent the flame front in the combustor from travelling forwardly into the swirl cup toward the fuel nozzle. The venturi also has an inner surface along which the fuel from the nozzle may form a film which may be airblast atomized by the swirl air flowing through the swirl cup.
In view of these many related components affecting combustion performance, it is desired to further improve combustor performance due to improved swirl cup design.
A swirl cup for a gas turbine engine combustor includes a tubular body having an inlet at one end for receiving a fuel injection nozzle, an outlet at an opposite end for discharging the fuel, and an annular septum therebetween. A row of first swirl vanes is attached to the septum adjacent the body inlet, and a row of second swirl vanes is attached to the septum adjacent the first swirl vanes and spaced upstream from the body outlet. Air from the first and second swirl vanes is swirled directly around the injected fuel without a flow barrier or venturi therebetween.